Velocity sensor firing mechanism for artillery weapons

ABSTRACT

In recoiling guns of the type wherein the firing thereof is accomplished during the forward travel of the recoiling parts, the problem of compensating for variations in the distance of recoil travel has been solved by a velocity sensor device disposed in the path of the flow of hydraulic fluid between the recuperator and recoil mechanisms and provided with a movable firing piston arranged to be actuated by the hydraulic flow thereagainst upon the attainment of sufficient momentum to overcome the predetermined resistance introduced into an adjustable mechanical linkage arrangement in direct ratio to the size of the propellant charge in the ammunition to be fired.

United States Patent [72] Inventors Jimmy H. Williams Bettendorf, Iowa; Lawrence L. Frauen, Moline, Ill. [21] Appl. No. 828,561 [22] Filed May 28, 1969 [45] Patented Mar. 2, 1971 [73 1 Assignee the United States of America as represented V by the Secretary of the Army [S4] VELOCITY SENSOR FIRING MECHANISM FOR Primary Examiner Benjamin A. Borchelt Assistant Examiner-Stephen C. Bentley Allomeys-l-larry M. Saragovitz, Edward J. Kelly, Herbert Ber] and Albert E. Arnold, Jr.

ABSTRACT: In recoiling guns of the type wherein the firing thereof is accomplished during the forward travel of the recoiling parts, the problem of compensating for variations-in the distance of recoil travel has been solved by a velocity sensor device disposed in the path of the flow of hydraulic fluid between the recuperator and recoil mechanisms and provided with a movable firing piston arranged to be actuated by the hydraulic flow thereagainst upon the attainment of sufficient momentum to overcome the predetermined resistance introduced into an adjustable mechanical linkage arrangement in direct ratio to the size of the propellant charge in the ammunition to be tired.

Patented March 2, 1971 3,566,740

8 Sheets-Sheet 2 EEEi-Eb- 9O 111mg;- H Wfl1inms Lawrence Llfiuuen N m .SM ME W J All M, x W ATTORNEYS Patented March 2, 1971 3,56,?4

8 Sheets-Sheet 5 INVENTORS Jimngr HI/Williams l11WrEnce.l FI 11uErL Han M. W an I If W Wierws Patented March 2,1971

8 Sheets-Sheet 5 I76 I36 98 I30 m m u 9 1 u N.I W H m J ATTORNEYS Patented March 2, 19% $566,740

8 Sheets-Sheet 7 INVENTORS Jimmy H.Wi11iums LTLWIETIICE Ll'ruuen Y cum 7M wimtwfiwy ATTORNEY5 Patented March 2, 1971 ,566,740

8 Sheets-Sheet 8 lNlVENTORS Jimmy Hwflliums Lawrence Lfruu ETL VELOCITY SENSOR FIRING MECHANISM FOR ARTKLLERY WEAPONS BACKGROUND OF THE INVENTION This invention relates to large caliber guns and, is more particularly directed to a hydraulic firing mechanism adapted to be automatically triggered during the forward travel of the recoiling parts toward battery position.

in order to provide the light weight and the degree of accuracy required of current artillery weapons, the recoil forces imparted to the trunnions which serve to connect the gun to a fixed mount or mobile carriage must be kept to a minimum. This has been previously accomplished by lengthening the recoil travel of the gun or by increasing the ability of the various buffer mechanisms utilized in the system to absorb the recoil and counterrecoil energies of the moving parts. However, the distance over which the guns in current use are permitted to recoil cannot be increased to any appreciable extent without the necessity for digging a suitable pit in the ground to provide clearance for the breech end or, in the alternative, reducing the maximum elevation at which the gun will be fired. Moreover, improvements in the energy-absorbing ability of the type of buffer and recoil mechanisms ordinarily utilized in artillery weapons generally necessitate undesirable increases in size and weight.

Accordingly, in the search for a new approach to the problem of reducing the reaction forces transmitted to the trunnions of large caliber guns such as howitzers of the towed or self-propelled types, it hasbeen proposed that firing be accomplished during the forward travel of the recoiling parts toward battery position. In an arrangement of this kind, a considerable portion of the energy produced upon the firing of a round of ammunition will be consumed in halting the forward momentum of the recoiling parts and thereby provide a corresponding reduction in the forces which drive these parts to the rear. This concept is referred to a out-of-battery firing and, although employed in the past on some experimental guns, has never been fully utilized in modern artillery due to the difficulties involved in determining the point at which firing should be initiated to produce a maximum reduction in the trunnion forces without detriment to the required recoil and counterrecoil functions thereof. This problem is particularly complicated by the necessity for frequently changing the range or elevation at which the gun is to be fired. In such instances, the recoil forces imparted to the trunnions of the gun will also change since firing at higher elevations involves increased gravity forces while firing at longer ranges requires heavier and more powerful propellant charges.

In previous guns arranged to fire out-of-battery," firing has been generally accomplished by a mechanical detent located at a fixed point on a stationary part of the cradle or mount. It was therefore necessary to adjust the recoil mechanism or buffer devices to compensate for changes in the elevation and range at which the firing was being accomplished. Where the recoil mechanism was hydraulically operated, it was also necessary to compensate for changes in the temperature and viscosity of the fluid being utilized therein. Another variable requiring corresponding adjustment of the recoil mechanism was the use of ammunition with propellant charges of different power. Consequently, the proper adjustment of the recoil mechanism required to compensate for some or all of the foregoing variables has been a difficult and complex requirement beyond the capability of previous guns which fire outof-battery." Furthermore, these variables occur so frequently during the use of artillery under modern combat conditions that even if the required adjustments could be made, they would certainly interfere with the desired rapidity with which the gun can be repetitively fired as well as the ability thereof to accurately track a movable target.

Accordingly, it is a primary object of this invention to provide an improved firing system for a large caliber gun of the type which utilizes hydraulic recoil and recuperator mechanisms and is arranged to be fired during forward movement of the recoiling parts toward battery position.

It is a further object of this invention to provide a firing mechanism for a gun, as aforesaid, which can be operated by the same hydraulic fluid utilized to function the recoil and recuperator mechanisms.

Another important object of the present invention is to provide a firing mechanism, as aforesaid, which will be positively triggered whenever the forward travel of the recoiling parts toward battery position attains a predetermined velocity.

It is another object of this invention to provide a firing mechanism, as aforesaid, wherein the triggering thereof will immediately terminate the acceleration being imparted to the forwardly moving parts thereby minimizing additional changes in the velocity thereof in the event of any extended delay in the ignition of the propellant charge.

A further object of this invention is to provide a hydraulic firing mechanism, as aforesaid, which will tolerate reasonable pressure variations in the recoil mechanism therefor and thereby avoid the need for regulators and other similar control devices.

It is a particular object of this invention to provide a firing mechanism, as aforesaid, which will automatically eliminate any variations in the forward velocity of the recoiling parts due to the angle of elevation of the gun tube at the instant of firing.

An additional object of this invention is to provide a firing mechanism, as aforesaid, which will initiate each firing cycle of the gun at the particular instant of time required to ensure sufficient recoil travel of the recoiling parts beyond the point at which such parts are latched against the forward travel required to initiate a new cycle of operation.

Another object of this invention is to provide a firing mechanism, as aforesaid, which will require one simple adjustment to compensate for any change in the propellant charge of the ammunition being fired in the gun.

Still another object of the present invention is to provide a firing mechanism, as aforesaid, which will provide a sensitive and consistently reliable response to the attainment of a predetermined forward velocity of the recoiling parts regardless of any changes in the temperature or viscosity of the hydraulic fluid being utilized.

SUMMARY OF THE INVENTION lt has been found that these objects can be achieved by a self-contained firing unit incorporated in the breech end of the gun in direct communication with the hydraulic fluid utilized in the recoil and recuperator mechanisms with which the gun is provided. When the gun is released from a rearward latched position, the recuperator mechanism forces hydraulic fluid through the firing unit and into the recoil mechanism to accelerate the gun in a forward direction toward battery position. A hollow piston in the interior of the firing unit is located in the path of the hydraulic flow and is arranged to be advanced thereby to actuate a linkage for imparting firing movement to a slidable trigger bar projecting from the firing unit. However, the linkage assembly is arranged to remain inoperative until the velocity of the hydraulic flow attains sufficient momentum to overcome the resistance of a spring-biased plunger acting through a fulcrumed lever. The degree to which the linkage will resist mechanical actuation can be readily set at a predetermined value corresponding to the size or power of the propellant charge in the particular ammuni tion being fired simply by moving the location of the fulcrum along the length of the lever. Once the rearward travel of the hollow piston is terminated, the flow of the fluid to the recoil mechanism is discontinued.

Since the gun will not fire until the forward velocity thereof is sufficient to force the hydraulic fluid through the firing unit with sufficient momentum to overcome the resistance of the hollow piston to rearward movement, any increase or decrease in the various factors which affect the forward travel of the gun will automatically provide a compensatory increase or decrease in the distance the gun will travel prior to reaching the required velocity. Thus, once the firing unit has been set to respond to the firing of ammunition with a given propellant charge, no further adjustment is required. During each firing the recoiling parts are latched in a stationary rearward position to permit the breech to be opened for the loading of a new round of ammunition into the firing chamber. As the breechblock is lifted to open the breech, the trigger bar in the firing unit is actuated thereby to reset the linkage and thereby return the fulcrumed lever and the hollow piston into position to permit initiation of the next firing cycle.

BRIEF DESCRIPTION OF THE DRAWINGS The exact nature of the invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification when read in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective left side view of a gun incorporating the present invention and shows the gun mounted in its cradle which is partially cut away to expose a portion of the recoil mechanism;

FIG. 2 is a fragmentary right side view of the breech end of the gun on a slightly larger scale than FIG. 1 and shows the gun in the latched rearward position with the firing unit having been reset during the elevation of the breechblock to the open position thereof;

FIG. 3 is a schematic diagram illustrating the arrangement of the recuperator and recoil mechanisms and showing the manner in which the firing unit is connected thereto to provide a closed fluid pressure system.

FIG. 4 is a vertical section taken along line 4-4 in FIG. 2 and enlarged to show the mounting details of the torque shaft which transfers the movement of the operating piston to the linkage arrangement utilized to actuate the trigger bar;

FIG. 5 is a vertical section taken along line 5-5 in FIG. 4 showing the fluid-filled interior configuration of the sensor block with the operating piston in the prefired position thereof;

FIG. 6 is a vertical section taken along line 6-6 in FIG. 4 to show details of the linkage arrangement utilized to convert rotation of the torque shaft to horizontal displacement of the trigger bar;

FIG. 7 is a horizontal section taken along line 7-7 in FIG. 6 to show further details of the linkage arrangement;

FIG. 8 is-a horizontal section taken along line 8-8 in FIG. 6 to show the means by which the operation of the linkage arrangement can be adjusted in accordance with the size of the propellant charge being utilized in the ammunition;

FIG. 9 is a vertical section taken along line 9-9 in FIG. 6 to show the details of the arrangement which permits the opening movement of the breechblock to reset the trigger bar and actuating linkage to the prefired position preparatory to the firing of the next round of ammunition;

FIG. 10 is a vertical section taken along line 10-10 in FIG. 6 to show the details of the plunger mechanism which provides the resistance required to prevent actuation of the sensor piston prior to the attainment of the desired forward velocity of the recoiling parts;

FIG. 11 is a vertical section through a sensor block taken along line 11-11 in FIG. 5 to show additional details of the interior configuration thereof;

FIG. 12 is a fragmentary view of FIG. 5 in which arrows indicate the flow path of hydraulic fluid through the sensor piston and into the exit port once the resistance thereof to forward movement has been overcome;

FIG. 13 is a sectional view similar to FIG. 6 but showing the position of the linkage arrangement during the firing advance of the trigger bar;

FIG. 14 is a perspective view of the housing for the linkage arrangement and is broken away to show the manner in which the adjustable fulcrum pin is mounted;

FIG. 15 is a perspective view of the trigger bar actuator;

FIG. 16 is a perspective view of the fulcrum lever; and

FIG. 17 is a perspective view of the spring-biased plunger utilized to resist the pivotal movement of the fulcrum lever.

Referring more particularly to the drawings wherein similar reference characters have been employed to designate corresponding parts throughout, the gun in which the present invention has been incorporated is a howitzer which can be separately towed or mounted on a self-propelled vehicle and consists basically of a breech ring 12 coupled to the breech end of a gun tube 14 by an adapted 16. All reference hereinafter to such terms of direction as forward, rearward," right" and left are based on the position of an observer standing at the breech end of gun tube 14 and looking in the direction in which the projectile will be fired. Tube 14 is fixedly secured within a cylindrical frame or sleigh 18 which is, in turn, slidably disposed in a cradle 20 provided with a U shaped interior. As best shown in FIGS. 1 and 1, this is accomplished by rollers 22 which are fixedly secured to opposite sides of frame 18 at forward and rearward locations thereon and project outwardly therefrom to ride on reinforced rail surfaces 24 extending along the top edges of the spaced vertical walls of cradle 20. The wall surfaces within the U-shaped interior of cradle 20 are respectively provided with opposed longitudinal tracks 26 for slidably receiving mating ribs 28 which project outwardly from the sides of frame 18 immediately below the rearwardly located rollers 22.

In order to furnish means for mounting cradle 20 in a mobile carriage (not shown), a pair of outwardly projecting trunnions 30 are respectively provided on opposite sides of cradle 20 adjacent the rear end thereof. A second set of trunnions 32 of smaller size are also provided on opposite sides of cradle 20 substantially midway along the length thereof to serve as the mounting point for a conventional elevating mechanism (not shown) arranged to vary the angle at which tube 14 is positioned at the instant the gun is fired. At the rear end of cradle 20, a tubular member 34 is centrally fixed in the bottom of the U-shaped interior for the purpose of retaining a piston rod 36 in a stationary position. This is accomplished by providing the rear end of piston rod 36 with a reduced diameter portion 37 of slightly greater length than that of tubular member 34 and inserting portion 37 through member 34 to protrude from the rear end thereof. A washer 38 is fitted onto the protruding rear end of portion 37 and a nut 40 is threaded thereon to force washer 38 into contact with the rear end of tubular member 34 thereby retaining piston rod 36 against movement relative to cradle 20.

Piston rod 36 is a component part of a hydraulic recoil mechanism 42 which includes a cylinder 44 fixedly mounted in a horizontal tubular housing 46 depending from the forward end of frame 18. The forward end of piston rod 36 is arranged to extend into cylinder 44 from the rear end thereof in a slidable but fluid-sealed manner and terminates in an enlarged head 48 of sufficient diameter to ensure slidable contact throughout the interior surface of cylinder 44. A forwardly extending opening 50 is axially provided in the body of piston rod 36 and is continued out through head 48 thereof in axial alignment with a fixed control rod 52 projecting rearwardly from the front wall surface of recoil'cylinder 44. The rear end of control rod 52 isconically tapered, as indicated at 54, to facilitate the entry thereof into an enlarged but correspondingly tapered entrance 56 located in piston head 48 at the front end of opening 50. The smaller rear end of entrance 56 is arranged to provide a clearance fit with control rod 52 for a purpose to be shown.

Recoil cylinder 44 is completely filled with a conventional hydraulic fluid such as recoil oil and, as best shown in FIG. 1, a suitable oil line 58 extends from the central portion of cylinder 44 into the side of the firing unit 60 of the present invention which is, in turn, connected to a recuperator mechanism 62 capable of imparting forward acceleration to the recoiling parts upon release thereof from a rearwardly latched position. Recuperator mechanism 62 includes a floating piston 64 slidably disposed within an elongated cylinder 66 which is supported above gun tube 14 and in coaxial relation therewith by a ring 68 extending upwardly from the forward end of frame 18. At a point forwardly of support ring 68, cylinder 66 is axially coupled to a forwardly extending pressure cylinder 70. Recoil cylinder 44 and pressure cylinder 70 are both fixedly attached to gun tube 14 by a common yoke 72.

Floating piston 64 is of the double-acting type and though disposed for reciprocating movement within the interiors of elongated cylinder 66 and pressure cylinder 70 is, nevertheless, suitably sealed to separate a rearward volume of hydraulic fluid from a forward volume of nitrogen gas charged to attain a nominal pressure of approximately 115 p.s.i. at the termination of the forward stroke of floating piston 64. At this time, the recoiling mass which consists of tube 14, frame 18, recoil cylinder 44 and recuperator mechanism 62, is retained in a recoiled rearward position by a latch 74 acting on the front end of each rib 28 on frame 18 as best shown in FIG. 2.

Thus, when latch 74 is pivoted out of engagement with ribs 28 by a lanyard 76, the compressed nitrogen gas in cylinder 70 acts on the front face of floating piston 64 to displace the oil in elongated cylinder 66. As is readily apparent from the schematic representation of FIG. 3, this displaced oil is forced into firing unit 60 through a flow cutoff device 77 and then through oil line 58 into the forward end of recoil cylinder 44. Since piston rod 36 is fixed to stationary cradle 20, the flow of oil forces recoil cylinder 44 forwardly thereby imparting corresponding movement to gun tube 14. As recoil cylinder 44 moves forwardly, the oil therein rearwardly of piston head 48 is forced through a plurality of radially spaced ports 78 in piston rod 36 into opening 50 therein and out through tapered entrance 56 into the expanding volume forwardly of piston head 48. When the recoiling mass reaches a predetermined forward velocity, firing until 60 will be actuated in a manner to be more fully explained hereinafter. Thereupon, the forces produced by the firing of the round of ammunition in gun tube 14 will initially halt the forwardly moving mass and thereafter impart recoil movement thereto. This change in direction of travel of the gun also reverses the flow of oil in recoil cylinder 44 since the subsequent reduction in the chamber volume forwardly of piston head 48 forces the oil therein out through line 58 and into firing unit 60. A conduit 80 in firing unit 60 bypasses cutoff device 77 and directs the flow of oil through a check valve 82 into the rear end of recuperator cylinder 66. The consequent increase of oil in recuperator mechanism 62 forces floating piston 64 forwardly to compress the nitrogen gas in pressure cylinder 7 0 during the entire rearward travel of the recoiling mass. As recoil cylinder 44 moves to the rear, the oil forwardly of piston head 48 is forced through tapered entrance 56 into opening 50 of piston rod 36 and out through radial ports 78 into the expanding volume rearwardly of piston head 48. At the same time, a suitable unidirectional valve 84 in piston head 48 permits a more limited flow of oil therethrough in the same direction.

As breech ring 12 recoils beyond latch 74, control rod 52 enters tapered entrance 56in piston head 48 thereby blocking opening 50 against any significant flow of oil therethrough. Since valve 84 then serves as the sole passage for the oil, the recoiling mass is gradually brought to a halt within approximately inches behind latch 74 by a suitable buffer mechanism (not shown). Thereupon, the accumulated pressure of the nitrogen gas in cylinder 70 forces additional oil into recoil cylinder 44 which begins to accelerate the recoiling mass in the forward direction. This reversal in the flow of oil closes valve 84 so that the only exit path for the oil from one side of piston head 48 to the other is through the limited annular clearance between control rod 52 and the smaller end of tapered entrance 56. Consequently, the flow of oil against the forward end of recoil cylinder 44 is drastically throttled thereby minimizing the forward velocity of the gun and reducing the shock imparted to latch 74 upon engagement therewith for retention in the position schematically shown in FIG. 3.

Upon release of latch 74, the gun begins to initiate another firing cycle and is forwardly accelerated, as previously explained, to attain the velocity required to actuate the flow cutoff device 77 in firing unit 60. Device77 is contained in a relatively square hollow block fixedly secured to the rear end of recuperator cylinder 66. A rectangular housing 92 with one sidewall completely removed is suitably bolted to the right side of block 90 to.form,an enclosure for the mechanically operated portion of firing unit 60. A trigger bar 94 is slidably mounted in housing 92 to protrude from the rear end thereof and is arranged to be rearwardly displaced by a depending arm 96 on an actuator 98 fixedly secured to one end of a torque shaft 100. As best shown in FIG. 4, shaft 100 is rotatably mounted in block 90 between an end bearing I02 and a thrust bearing 104, both of which are threadably secured in opposite sides of block 90 for easy removal therefrom. Shaft 100 is extended to protrude from the side of block 90 into housing 92 and terminate in a squared end 106 engageable in a mating hole 108 passing through the upper portion of actuator 98. Thrust bearing 104 is also provided with a roller bearing 110 for supporting the protruding end of shaft 100.

Extending forwardly from actuator 98, as shown in FIG. 15, is a second arm 112 provided with a transversely projecting pin 114 adjacent the front end thereof. A transfer member 116 is rotatably mounted on a cylindrical stud 118 fixed in the outer side of housing 92 and extending transversely into the interior thereof. As best shown in FIG. 14, transfer member 116 consists of a substantially rectangular base 120 and a vertical arm 122 of T-shaped cross section extending upwardly from the end in which stud 118 is located. The opposite end of base 120 is provided with a forwardly opening transverse slot 124 therethrough arranged to rotatably receive pin 114 on actuator 98. Projecting rearwardly from T-shaped arm 122 is a wing 126 formed as a quadrant and positioned so that the arcuate exterior periphery 128 thereof will contact a follower roller 130 mounted at the forward end of a fulcrum lever 132 (FIG. 13). The top of arm 122 terminates below arcuate periphery 128 to form a forwardly facing incline 134 which provides a seat for follower roller 130 and also serves as a cam surface for lifting such roller to free transfer member 116 for pivotal movement. As member 116 is pivoted, arcuate periphery 128 thereon retains follower roller 130 in the raised position thereof without interfering with the free pivotal movement required of transfer member 116.

The rearward portion of fulcrum lever 132 is reduced in width, as indicated at 136 in FIG. 16 to provide access for a link 138 pivotally mounted at the forward end thereof to a fixed pin 140 extending into the interior of housing 92 from the outer sidewall thereof. The rearward end of link 138 is provided with a laterally projecting pin 142 rotatably engageable in a suitable hole 143 in the rearward end of fulcrum lever 132. Thus, link 138 retains fulcrum lever 132 against longitudinal movement while lateral movement thereof is prevented by the contact with the upper rectangular end of a cylindrical casing 146 vertically fixed in housing 92 for a purpose to be shown. However, such retention of fulcrum lever 132 in housing 92 does not prevent the tilting thereof in response to the vertical force imparted to follower roller 130 by the clockwise rotation of transfer member 116 or in response to the vertical force imparted to the opposite end of fulcrum lever 132 by a spring-biased vertically disposed plunger 144.

As best shown in FIG. 6, plunger 144 is contained in the previously-mentioned cylindrical casing 146 which is, in turn, fitted into an open rectangular recess 148 vertically provided in a lateral interior extension 150 of the rear end wall of housing 92. The upper end of plunger casing 146 terminates in an L-shaped section 152 in which the horizontal leg 154 is greater in width than vertical recess 148 and consequently sits on the shelf formed by the top of the sidewall extension 150 of housing 92. In this position, a portion of section leg 154 extends into a mating slot 156 in the outer sidewall of housing 92 to lock plunger casing 146 against vertical movement. Lateral movement of plunger casing 146 in recess 148 is prevented by contact between the vertical leg 158 of L-shaped section 152 and the exterior surface of sensor block 90. Vertical downward displacement of plunger 144 is resisted by a surrounding coil spring 160 seated at the lower end thereof over a vertical boss 162 in the bottom of cylindrical casing 146, as shown in FIG. 10, and bearing against the annular shoulder formed by an enlarged head 164 at the upper end of plunger 144. However, the extent of vertical movement of plunger 144 is limited by a stop pin 166 extending through enlarged head 164 to engage in vertical slots 168 provided in opposite sides of plunger casing 146. The upper end of plunger 144 is wedge shaped, as indicated at 170, to provide'a relatively narrow area of contact with the underside of fulcrum lever 132. An exteriorly knurled knob 172 is threadably secured to the lower .,end. of plunger casingfi146 to provide means for adjusting the tension of spring 160 so as to establish the proper preload thereof prior to final assembly in housing 92. The lower end of open recess 148 is enlarged, as indicated at 174 in FIG. 14, to provide clearance for adjusting knob 172.

The amount of force required to pivot fulcrum 132 is also controlled by the position of a pin 176 extending through a longitudinal slot 177 into the interior of housing 92 in contact with the upper edge of lever 132. Pin 176 is fixed in a slide 178 which is, in turn, slidably mounted in a bracket 180 suitably bolted, as shown at 181 in FIG. 10, to the top and side of housing 92. The interior of bracket 180 is provided with longitudinal parallel tracks 182 arranged to slidably receive elongated arms 184 extending from the opposite ends of slide 178. In addition, bracket 180 includes an elongated longitudinal slot 186 in the outer side thereof which will permit the required extent of longitudinal travel of slide 178. Slide 178, as best illustrated in FIG. 8, is also provided with a plunger type of detent 188 disposed rearwardly of and parallel to fulcrum pin 176 for selective engagement with a plurality of recesses 190 longitudinally spaced along the side of housing 92. A spring 191 biases the end of detent 188 into the selected one of recesses 190 while a control knob 194 on the other end of detent 188 extends beyond bracket 180 to provide a means for effecting manual withdrawal thereof from the recess 190 engaged therewith. Control knob 194 can also be utilized as a handle for moving slide 178 longitudinally within bracket 180 to change the location of detent 188 from one recess 190 to another. As is readily apparent, any change in the position of slide 178 effects a corresponding changein the position of fulcrum pin 176 which changes the length of the moment arm of lever 132 relative to the point of contact with plunger 144 and consequently varies the force necessary to rotate cam surface 134 past the blocking contact of follower roller 130. Each recess 190 is specifically located so that fulcrum lever 132 will produce a predetermined degree of resistance to the initial pivotal movement of actuator 98 corresponding to the weight of the propellant charge utilized in the ammunition being fired.

The end of shaft 100 within the interior of block 90 also terminates in a squared portion 192 on which a blocking arm 195 is fixedly secured to extend downwardly into the longitudinal path of cutoff device 77. As shown in FIG. 5, device 77 consists of a hollow piston 196 slidably disposed in a mating cylindrical chamber 198. Piston 196 is closed at the rear end thereof and the exterior face of such closed end is angularly cut away as indicated at 200 to form a rearwardly extending ledge 202 located slightly above the central longitudinal axis of piston 196. The forward edge of blocking arm 195 is provided with a V-shaped notch 204 arranged to receive the rear corner of ledge 202. The lower wall surface of notch 204 is arcuately formed to blend into the downwardly continuing arcuate surface 206 on the forward edge of arm 195. Such construction permits the corner of ledge 202 to enter into notch 204 during the rearward pivotal movement of blocking arm 195 and to move out of notch 204 during the pivotal return of arm 195 to a substantially vertical position. In order to prevent rotation of piston 196 in chamber 198, the closed rear end of piston 196 is provided with a longitudinal hole 208 for slidable reception of a fixed pin 210 protruding from a stop surface 212 extending forwardly from a plug 213 fixedly secured in the rear wall of block to close the opening through which cutoff device 77 is arranged to be assembled and disassembled. The interior rear wall of hollow piston 196 is conically shaped to form a thrust surface 214 for reversing the flow of oil entering into piston 196 from the open front end thereof. In order to provide an exit'for the oil in the interior of piston 196, a plurality of circumferentially elongated slots 216 are radially spaced about the body thereof, as best shown in FIG. 11.

The forward end of piston chamber 198 communicates with an offset channel 218 leading into an inlet 220 of equivalent diameter which connects with the interior of recuperator cylinder 66. Fixedly mounted in the forward end of piston chamber 198 is a tubular extension 222 of lesser diameter which projects into the interior of hollow 'pistonl96' to'ter minate slightly beyond the location of slots 216 therein in the preactuated position of piston 196. An annular collector channel 224 is provided in the interior wall surface of piston chamber 198 to surround piston 196 in communication with slots 216 therein. Channel 224 is arranged to intersect the lower end of a vertical hole 226 provided in the top of sensor block 90 to permit the interior thereof to be filled with the oil. Filler hole 226 is, in turn, intersected by an exit port 228 extending laterally into block 90 from the left-hand side thereof. A second vertical oil filler hole 230 is provided in the, top of block 90 rearwardly of filler hole 226 and parallel thereto and is vertically extended to intersect the rear end of piston chamber 198. Oil filler holes 226 and 230 are additionally connected by conduit'80. I

The interior of block 90 is additionally connected to the rear end of recuperator cylinder 66 by an exit passage 232 disposed above and parallel to the passage formed by channel 218 and inlet 220. The entrance to passage 232 is controlled by check valve 82 consisting of a plunger type hollow body 236 with a diametrically enlarged head 238 at the rear end thereof in abutment with the rear end of a coil spring 240. The front end of coil spring 240 is seated against a bushing 241 suitably fixed in passage 232. Plunger head 238 is formed with a rearwardly facing valve seat 242 having a rounded contact surface 244 engageable, in response to the urging of spring 240, in a mating entrance 246 provided in the forward portion of conduit 80. Valve seat 242 is provided with a central relief hole 250 therethrough opening into communication with the hollow interior of plunger body 236.

' As will be explained in greater detail hereinafter, when the flow of oil through block 90 attains the velccity required to overcome the resistance set into sens'or device 77, shaft is rotated to pivot actuator 98 and thereby displace trigger bar 94 rearwardly to function a scar release 251 protruding forwardly from the interior of breech ring 12. In order to fire another round of ammunition, it is necessary to reset sensor device 77 so that piston 196 will be in contact with the front end wall of chamber 198 thereby permitting blocking arm to assume the vertical position shown in FIG. 5. Accordingly, a bracket 252 is fixedly secured to the rear end of housing 92 and extends rearwardly therefrom above breech ring 12 to terminate in a depending slotted end 254 as best shown in FIGS. 2 and 6. A double-armed crank 256 is pivotally pinned to end 254 of bracket 252 with the upper arm of crank 256 extending into the vertical path of a breechblock 258 slidably mounted in breech ring 12 to provide the opening and closing of the breech required to load a round of ammunition into firing position. The lower end of crank 256 is secured to the rear end of an elongated rod 260 which is, in turn, fixedly attached at the opposite end thereof to the upper end of a reset lever 262 pivotally mounted on a rearwardly projecting boss 264 at the bottom of bracket 252 at a point above trigger bar 94. The lower end of lever 262 is bifurcated, as indicated at 266 in FIG. 9, to straddle trigger bar 94 and contact the rear face of a washer 268 fixedly secured thereon. Thus, when trigger bar 94 is actuated to depress sear release 251, washer 268 is moved into contact with the bifurcated end 266 of reset lever 262 to pivot such lever to a vertical position. During this movement of lever 262, elongated rod 260 is pulled forwardly to pivot the upper arm of crank 256 into the vertical path of breechblock 258. When breechblock 258 is raised to open the breech, crank 256 is pivoted thereby in a clockwise direction, as shown in FIG. 2, to return trigger bar 94 and the reset mechanism associated therewith to the prefired position shown in FIG. 6.

As previously mentioned, once latch 74 is actuated to release the recoiling mass for forward movement, the compressed gas in recuperator cylinder 70 initiates a flow of oil therefrom through firing unit 61) and into recoil cylinder 44. The oil enters sensor block 90 through offset channel 220 and then flows into tubular extension 222 to be directed thereby against conical thrust surface 214 in hollow piston 196. As indicated by the arrows in FIG. 12, thrust surface 214 reverses the flow of oil by a full 180 without any appreciable loss in momentum. The continuing entry of oil into piston 196 from the rear end of tubular extension 222 diverts the reverse fiow into the annular space between the exterior of extension 222 and the interior of piston 196. Since such annular space is closed by the front end wall of chamber 198, the reverse flow of fluid is diverted an additional 90- through slots 216 in piston 196 into collector channel 224 and thence into filler hole 226 for eventual exit from sensor block 90 by means of port 228 therein. However, the initial momentum of the oil flow acts on piston 196 to impart a rearward thrust on blocking arm 195 and generate torque in shaft 100. In view of the 270 change in direction of the flow of oil, a large amount of torsional energy is imparted to shaft 100 by a relatively low rate of flow.

When the torque on shaft 100 exceeds the resisting force being exerted on inclined cam surface 134 of transfer member 116 by fulcrum lever 132 in response to the spring bias of plunger 144, transfer member 116 will be pivoted to free actuator 98 for imparting firing movement to trigger bar 94. Once pivotal movement of actuator 98 has been initiated, the corresponding pivotal movement of blocking arm 195 permits piston 196 to move freely in response to the momentum of the continuing flow of oil therethrough. However, by the time piston 196 reaches stop surface 212, slots 216 are completely blocked by the interior wall surface of chamber 198. Thus, the flow of oil through sensor block 90 to recoil mechanism 42 is discontinued thereby terminating the acceleration being imparted to the recoiling mass. This feature prevents any undesirable increase in the velocity of the recoiling mass in the event of any appreciable delay between the time at which the primer in the round being fired is struck by the firing pin and the time required to ignite the entire propellant charge. Since the closing of slots 216 in piston 196 halts the further entry of oil into passage 218, the flow from recuperator mechanism 62 is shunted into passage 232 to pass through relief hole 250 in check valve 82 for exit through port 228. Thus, check valve 82 creates a pressure differential between the inlet and outlet flow of oil through sensor block 90 which can be utilized to provide the energy necessary to complete the function of all the parts involved in the firing of the gun. in the event of a failure to fire by the time the forward travel of the recoiling mass has reached a predetermined distance beyond the maximum at which the firing should have taken place, a suitable buffer mechanism (not shown) can be attached to frame 18 to initiate the decelerating action required to reduce the dangerous impact which would otherwise be imparted to cradle 20 as the recoiling mass reaches battery position. If this eventuality does take place due to a defective round, the return of the recoiling mass to the rearwardly latched position can be obtained by replacing the defective round with a new round of sufficient power to ensure full recoil the particular elevation ofthe gun tube and then actuating trigger bar 94 manually or by a separate mechanical device operative on sear release 251 in breech ring 12.

During the relatively short rearward travel of piston 196, blocking arm 195 is pivoted to rotate shaft 100 and impart corresponding pivotal movement to actuator 98 for functioning trigger bar 94. As best shown in FIG. 13, the clockwise pivotal movement imparted to actuator 98 causes pin 114 thereof to ride along transverse slot 124 in base of transfer member 116 and impart corresponding pivotal movement thereto. The maximum resistance to the pivotal movement of actuator 98 is produced during the interval in which the follower roller is forced upwardly by cam surface 134 out of contact therewith. During the remainder of the pivotal movement of actuator 98, transfer member 116 is freely pivoted about pin 118 while the arcuate periphery of wing 126 retains follower roller 130 and thereby fulcrum lever 132 in the position imparted thereto by cam surface 134.

As the rearward travel of piston 196 is converted to actuation of trigger bar 94, sear release 251 in breech ring 12 is displaced to fire the chambered round of ammunition in the gun tube 14 and provide the forces necessary for reversing the direction of travel of recoil cylinder 44 and of the flow of oil through firing unit 60. Since slots 216 in piston 196 are closed, the only exit for the reversed flow of oil through block 90 is the relatively small relief hole 250 in check valve 82. However, since relief hole 250 is too small to accommodate the entire flow of oil into block 90 at this time, the resulting pressure increase acts against plunger head 238 to overcome the bias of coil spring 240 and open check valve 832. Thus, the flow of oil into sensor block 90 will exit through passage 232 and act on floating piston 64 in recuperator cylinder 66 to compress the nitrogen gas contained in pressure cylinder 70. The rearward travel of the recoiling mass is finally arrested by the previously described operation of recoil cylinder 44 in conjunction with a pair of conventional buffer elements (not shown) arranged to be energized by the passage of breech ring 12 beyond latch 74. Thereupon, the pressure of the nitrogen gas in recuperator mechanism 62 will begin to accelerate the recoiling mass forwardly at a relatively slow rate, as explained hereinbefore, until halted by engagement with latch 74. At this time, the breech can be opened to permit the loading ofa new round of ammunition. As previously described, the opening movement of breechblock 258 serves to reset trigger bar 94 and flow cutoff device 77 to the prefiring position of FIGS. 5 and 6 thereby permitting another firing cycle to be initiated by the pulling of lanyard 76.

While the invention described herein provides a relatively simple and reliable mechanism of rugged construction, the outstanding feature thereof is an extremely sensitive response to the attainment of a predetermined flow velocity of hydraulic fluid corresponding to the forward velocity of the recoiling mass toward battery position. This desirable sensitivity is obtained without the need for complicated controls or pressure regulating devices and, in addition, does not require any greater rate of flow than that required to function the ordinary recoil and recuperator mechanism utilized in the larger caliber artillery weapons. Furthermore, the entire firing mechanism can be completely housed in a single unit which, in turn, can be connected to the recoil and recuperator mechanisms in a manner which provides a completely closed hydraulic system wherein compensation for any changes in the temperature or viscosity of the fluid therein can be readily effected. Another significant feature of the firing mechanism is its ability to immediately and completely remove the accelerating force on the forwardly moving recoiling mass once the predetermined velocity has been attained. Thus, the delay usually encountered between the ignition of the primer and the combustion of the propellant charge does not increase the forward velocity of the recoiling mass beyond that attained at the initiation of firing.

Furthermore, the firing mechanism of the present invention incorporates simple and positive means for accurately changing the velocity at which firing will be initiated. As a result, the operator of the gun can readily compensate for any increase or decrease in the weight or energy level of the propellant charge. Any change in the elevation of the gun will, of course, produce a corresponding change in the gravity forces acting on the gun which will be reflected in an automatic increase or decrease in the distance traveled thereby prior to the attainment of the required velocity. Such arrangement provides a unique and highly desirable solution to the problem of compensating for changes in the forward velocity of the recoiling mass caused by the various variables encountered during the firing cycle. Moreover, the ability to lengthen or shorten the firing cycle by controlling the forward velocity required of the recoiling mass prior to the initiation of firing is a factor which has solved the previous difficulties encountered with out-ofbattery guns. Since these guns were usually designed to fire upon reaching a fixed distance during the forward travel toward battery, the required control of the recoil and counterrecoil energies of the gun could be accomplished only by proper adjustment of the recoil mechanism or of suitable buffer devices associated therewith. However, such procedure does not permit automatic compensation for changes in elevation and consequently requires a frequency of adjustment which cannot be tolerated in view of the more rapid rate of fire required in modern combat.

We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

We claim:

1. In a gun having hydraulic recoil and counterrecoil means, latch means for releasably retaining the gun in a recoiled position, and means for firing the gun during the counterrecoil travel imparted thereto following the release thereof by the latch means, the improvement of means for delaying the firing of the gun until the counterrecoil travel thereof attains sufficient velocity to absorb a maximum of the recoil forces imparted thereto during the firing thereof and yet permit the remaining forces to return the gun into engagement with the latch means, said delay means comprising:

a thrust surface slidably disposed in the path of the hydraulic flow from the counterrecoil to the recoil means for imparting longitudinal displacement to the means for firing the gun;

lever means disposed for pivotal movement about a fulcrum point in position to oppose slidable movement of said thrust surface; and

means for selectively positioning the fulcrum point of said lever means to vary the opposition thereof to the slidable movement of said thrust surface in accordance with the size of the propellant charge utilized in the ammunition to be fired by the gun.

2. The combination defined in claim 1 including springbiased plunger means for imparting pivotal movement to said lever means, and means for adjusting the bias of said plunger means to supplement said lever means in opposing slidable movement of said thrust surface.

3. The combination defined in claim 1 including means for terminating the hydraulic flow against said thrust surface during the longitudinal movement imparted thereto to prevent any increase in the counterrecoil velocity of the gun during the interval between the firing of the propellant charge and the completion of combustion thereof.

4. The combination defined in claim 1 including means operative during the retention of the gun in the latched position thereof for returning said thrust surface to the position occupied thereby prior to the displacement of the means for firing the gun.

5. The combination defined in claim 1 wherein the means for firing the gun includes a slidable trigger and means for transmitting the movement of said thrust surface to said trigger.

6. in a gun having a hydraulic system including a recoil mechanism for halting the recoil travel thereof and a recuperator mechanism for imparting counterrecoil travel thereto, means for releasably latching the gun upon completion of the recoil travel thereof, and means for firing the gun during the counterrecoil travel imparted thereto following the release thereof from said latch means, the firing means comprising:

a housing interposed between the recoil and recuperator mechanisms in hydraulic connection therewith;

slidable trigger means disposed within said housing to pro ject exteriorly thereof;

linkage means pivotally mounted within said housing for actuating said trigger means;

lever means mounted for pivotal movement about a fulcrum point in said housing for contact with said linkage means;

spring-biased plunger means for pivoting'said lever means about said fulcrum point to oppose pivotal movement of said linkage means;

a thrust surface slidably disposed in the path of the hydraulic flow from the recuperator mechanism to the recoil mechanism for imparting pivotal movement to sad linkage means; and

means for selectively positioning the fulcrum point of said lever means to vary the opposition thereof to the pivotal movement of said linkage means in accordance with the size of the propellant charge in the ammunition to be fired and thereby delay the actuation of said trigger means until the counterrecoil travel of the gun attains sufficient velocity to absorb the recoil energy in excess of the minimum amount required to return the gun into engagement with the releasable latch means.

7 The firing means as in claim 6 wherein said lever means is positioned intermediate said plunger means and said linkage means for simultaneous contact therewith and said linkage means is free to pivot while in contact with said lever means.

8. The firing means as in claim 6 wherein said spring-biased plunger means includes means for varying the pivotal force imparted to said lever means.

9. The combination defined in claim 6 wherein said means for firing the gun includes a blocking arm pivotally disposed in the slidable path of said thrust surface, and means for connecting said blocking arm to said linkage means for joint movement therewith.

10. The combination defined in claim 6 wherein said linkage means comprises:

a pivotal actuator for imparting slidable movement to said trigger means;

a transfer member pivotally mounted in said housing and having a cam surface thereon engageable with aid lever means; and

means for pivoting said actuator to impart pivotal movement to said transfer member whereby said cam surface thereon pivots said lever about said fulcrum point against the bias of said plunger means.

11. The combination defined in claim 6 including a reset lever pivotally mounted to the exterior of said housing in position to engage with said trigger means, and means for pivoting said reset lever, during the interval in which the gun is latched in the recoiled position thereof, to return said trigger means to the preactuated position thereof.

12. In a gun having a hydraulic system including a recoil mechanism for halting the recoil travel thereof and a recuperator mechanism for imparting counterrecoil travel thereto, means for releasably latching the gun upon the completion of the recoil travel thereof, and means for firing the gun during the counterrecoil travel imparted thereto following the release thereof from said latch means, the firing means comprising:

a housing having an inlet port in hydraulic communication with the recuperator mechanism and an exit port in hydraulic communication with the recoil mechanism,

a trigger slidably mounted in said housing to project outwardly therefrom;

a hollow piston slidably disposed in said housing and having a thrust surface in the path of the hydraulic flow from said inlet port for reversing the direction of flow, said piston having a plurality of radially disposed exit openings in the exterior periphery thereof for directing the reverse flow of fluid toward said exit port in said housing;

means for converting slidable movement of said hollow piston to firing actuation of said trigger; and

means in said housing for exerting a predetermined force opposing the slidable movement of said piston to delay actuation of said trigger until the counterrecoil travel of the gun attains the velocity at which the reversal of the hydraulic flow within said piston produces sufficient momentum on said thrust surface to overcome the force opposing the slidable movement thereof.

13. The combination defined in claim 12 wherein said thrust surface is formed by a conical end wall within the hollow interior of said piston, and said radially disposed exit openings are longitudinally located in said piston to communicate with said exit port in said housing prior to the slidable movement of said piston.

14. The combination defined in claim 12 wherein said housing includes a cylindrical chamber for slidably receiving said hollow piston and means for connecting said chamber to said exit port to provide a passage for the hydraulic flow.

15. The combination defined in claim 12 including means for blocking said exit openings in said hollow piston to discontinue the hydraulic flow therethrough during the slidable movement thereof and thereby terminate the acceleration being imparted to the gun by the recuperator mechanism, and valve means in said housing for providing a passage therethrough for the hydraulic flow exiting from the recoil mechanism during the recoil travel of the gun.

16. The combination defined in claim 12 wherein said means for converting slidable movement of said hollow piston to actuation of said trigger comprises:

a blocking arm pivotally mounted in said housing to depend into the slidable path of said hollow piston;

an actuator pivotally mounted in said housing for imparting slidable firing movement to said trigger; and

a torque-shaft having one end thereof fixedly secured to said blocking arm and having the other end thereof similarly secured to said actuator for directly transmitting the pivotal movement of said blocking arm thereto.

17. The combination defined in claim 12 wherein said means for exerting the predetermined force opposing the slidable movement of said hollow piston comprises:

a spring-biased plunger vertically mounted in said housing above said trigger; v

a torque shaft fixedly secured at one end thereof to said actuator, a blocking arm fixedly secured to the opposite end of said torque shaft in the slidable piston;

a transfer member having an inclined cam surface atthe upper end thereof and being pivotally mounted in said housing in position to respond to the movement of said means for actuating said trigger;

a lever pivotally mounted within said housing with one end in contact with said plunger, the other end of said lever having a follower roller in contact with said cam surface on said transfer member whereby the vertical bias of said plunger pivots said lever to oppose pivotal movement of said transfer member out of contact with said follower roller;

a fulcrum pin disposed in said housing in abutment with the upper edge of said lever; and

means for selectively locking said fulcrum pin in one of a plurality of predetermined locations corresponding to the various sizes of the propellant charge in the ammunition to be fired in the gun.

18. The combination defined in claim 17 wherein said last mentioned means comprises:

a bracket secured to the exterior of said housing;

a slide disposed in said bracket for longitudinal movement therein and adapted to serve as a carrier for said fulcrum pin;

a retractable detent transversely mounted in said slide;

a spring normally biasing said detent to project from said slide; and

said housing having a plurality of recesses adjacent said slide individually engageable with the projecting end of said detent to lock said slide and thereby said fulcrum pin in a stationary position, each of said recesses being longitudinally spaced from a line passing through thevertical axis of said vertically mounted plunger to position said fulcrum pin so that the opposition of said lever to the pivotal movement of said transfer member will vary in ac cordance with the counterrecoil velocity required by the gun to absorb the recoil energy produced by the firing thereof and still permit sufficient recoil travel to engage with the releasable latch means.

path of said hollow 

1. In a gun having hydraulic recoil and counterrecoil means, latch means for releasably retaining the gun in a recoiled position, and means for firing the gun during the counterrecoil travel imparted thereto following the release thereof by the latch means, the improvement of means for delaying the firing of the gun until the counterrecoil travel thereof attains sufficient velocity to absorb a maximum of the recoil forces imparted thereto during the firing thereof and yet permit the remaining forces to return the gun into engagement with the latch means, said delay means comprising: a thrust surface slidably disposed in the path of the hydraulic flow from the counterrecoil to the recoil means for imparting longitudinal displacement to the means for firing the gun; lever means disposed for pivotal movement about a fulcrum point in position to oppose slidable movement of said thrust surface; and means for selectively positioning the fulcrum point of said lever means to vary the opposition thereof to the slidable movement of said thrust surface in accordance with the size of the propellant charge utilized in the ammunition to be fired by the gun.
 2. The combination defined in claim 1 including spring-biased plunger means for imparting pivotal movement to said lever means, and means for adjusting the bias of said plunger means to supplement said lever means in opposing slidable movement of said thrust surface.
 3. The combination defined in claim 1 including means for terminating the hydraulic flow against said thrust surface during the longitudinal movement imparted thereto to prevent any increase in the counterrecoil velocity of the gun during the interval between the firing of the propellant charge and the completion of combustion thereof.
 4. The combination defined in claim 1 including means operative during the retention of the gun in the latched position thereof for returning said thrust surface to the position occupied thereby prior to the displacement of the means for firing the gun.
 5. The combination defined in claim 1 wherein the means for firing the gun includes a slidable trigger and means for transmitting the movement of said thrust surface to said trigger.
 6. In a gun having a hydraulic system including a recoil mechanism for halting the recoil travel thereof and a recuperator mechanism for imparting counterrecoil travel thereto, means for releasably latching the gun upon completion of the recoil travel thereof, and means for firing the gun during the counterrEcoil travel imparted thereto following the release thereof from said latch means, the firing means comprising: a housing interposed between the recoil and recuperator mechanisms in hydraulic connection therewith; slidable trigger means disposed within said housing to project exteriorly thereof; linkage means pivotally mounted within said housing for actuating said trigger means; lever means mounted for pivotal movement about a fulcrum point in said housing for contact with said linkage means; spring-biased plunger means for pivoting said lever means about said fulcrum point to oppose pivotal movement of said linkage means; a thrust surface slidably disposed in the path of the hydraulic flow from the recuperator mechanism to the recoil mechanism for imparting pivotal movement to sad linkage means; and means for selectively positioning the fulcrum point of said lever means to vary the opposition thereof to the pivotal movement of said linkage means in accordance with the size of the propellant charge in the ammunition to be fired and thereby delay the actuation of said trigger means until the counterrecoil travel of the gun attains sufficient velocity to absorb the recoil energy in excess of the minimum amount required to return the gun into engagement with the releasable latch means.
 7. The firing means as in claim 6 wherein said lever means is positioned intermediate said plunger means and said linkage means for simultaneous contact therewith and said linkage means is free to pivot while in contact with said lever means.
 8. The firing means as in claim 6 wherein said spring-biased plunger means includes means for varying the pivotal force imparted to said lever means.
 9. The combination defined in claim 6 wherein said means for firing the gun includes a blocking arm pivotally disposed in the slidable path of said thrust surface, and means for connecting said blocking arm to said linkage means for joint movement therewith.
 10. The combination defined in claim 6 wherein said linkage means comprises: a pivotal actuator for imparting slidable movement to said trigger means; a transfer member pivotally mounted in said housing and having a cam surface thereon engageable with aid lever means; and means for pivoting said actuator to impart pivotal movement to said transfer member whereby said cam surface thereon pivots said lever about said fulcrum point against the bias of said plunger means.
 11. The combination defined in claim 6 including a reset lever pivotally mounted to the exterior of said housing in position to engage with said trigger means, and means for pivoting said reset lever, during the interval in which the gun is latched in the recoiled position thereof, to return said trigger means to the preactuated position thereof.
 12. In a gun having a hydraulic system including a recoil mechanism for halting the recoil travel thereof and a recuperator mechanism for imparting counterrecoil travel thereto, means for releasably latching the gun upon the completion of the recoil travel thereof, and means for firing the gun during the counterrecoil travel imparted thereto following the release thereof from said latch means, the firing means comprising: a housing having an inlet port in hydraulic communication with the recuperator mechanism and an exit port in hydraulic communication with the recoil mechanism; a trigger slidably mounted in said housing to project outwardly therefrom; a hollow piston slidably disposed in said housing and having a thrust surface in the path of the hydraulic flow from said inlet port for reversing the direction of flow, said piston having a plurality of radially disposed exit openings in the exterior periphery thereof for directing the reverse flow of fluid toward said exit port in said housing; means for converting slidable movement of said hollow piston to firing actuation of said trigger; and means in said housing for exerting a predetermined force opposing the slidable movement of said piston to delay actuation of said trigger until the counterrecoil travel of the gun attains the velocity at which the reversal of the hydraulic flow within said piston produces sufficient momentum on said thrust surface to overcome the force opposing the slidable movement thereof.
 13. The combination defined in claim 12 wherein said thrust surface is formed by a conical end wall within the hollow interior of said piston, and said radially disposed exit openings are longitudinally located in said piston to communicate with said exit port in said housing prior to the slidable movement of said piston.
 14. The combination defined in claim 12 wherein said housing includes a cylindrical chamber for slidably receiving said hollow piston and means for connecting said chamber to said exit port to provide a passage for the hydraulic flow.
 15. The combination defined in claim 12 including means for blocking said exit openings in said hollow piston to discontinue the hydraulic flow therethrough during the slidable movement thereof and thereby terminate the acceleration being imparted to the gun by the recuperator mechanism, and valve means in said housing for providing a passage therethrough for the hydraulic flow exiting from the recoil mechanism during the recoil travel of the gun.
 16. The combination defined in claim 12 wherein said means for converting slidable movement of said hollow piston to actuation of said trigger comprises: a blocking arm pivotally mounted in said housing to depend into the slidable path of said hollow piston; an actuator pivotally mounted in said housing for imparting slidable firing movement to said trigger; and a torque shaft having one end thereof fixedly secured to said blocking arm and having the other end thereof similarly secured to said actuator for directly transmitting the pivotal movement of said blocking arm thereto.
 17. The combination defined in claim 12 wherein said means for exerting the predetermined force opposing the slidable movement of said hollow piston comprises: a spring-biased plunger vertically mounted in said housing above said trigger; a torque shaft fixedly secured at one end thereof to said actuator, a blocking arm fixedly secured to the opposite end of said torque shaft in the slidable path of said hollow piston; a transfer member having an inclined cam surface at the upper end thereof and being pivotally mounted in said housing in position to respond to the movement of said means for actuating said trigger; a lever pivotally mounted within said housing with one end in contact with said plunger, the other end of said lever having a follower roller in contact with said cam surface on said transfer member whereby the vertical bias of said plunger pivots said lever to oppose pivotal movement of said transfer member out of contact with said follower roller; a fulcrum pin disposed in said housing in abutment with the upper edge of said lever; and means for selectively locking said fulcrum pin in one of a plurality of predetermined locations corresponding to the various sizes of the propellant charge in the ammunition to be fired in the gun.
 18. The combination defined in claim 17 wherein said last mentioned means comprises: a bracket secured to the exterior of said housing; a slide disposed in said bracket for longitudinal movement therein and adapted to serve as a carrier for said fulcrum pin; a retractable detent transversely mounted in said slide; a spring normally biasing said detent to project from said slide; and said housing having a plurality of recesses adjacent said slide individually engageable with the projecting end of said detent to lock said slide and thereby said fulcrum pin in a stationary position, each of said recesses being longitudinally spaced from a line passing through the vertical axis of said vertically mounted plunger to position said fulcrum pin so that the opposition of said lever to the pivotal movement of said transfer member will vary in accordance with the counterrecoil velocity required by the gun to absorb the recoil energy produced by the firing thereof and still permit sufficient recoil travel to engage with the releasable latch means. 